The invention relates to the recording and reproduction of image information (video). More in particular, the present invention relates to the general problem of reproducing the recorded image information at a speed other than the normal speed.
As is known, video images (frames) are reproduced in accordance with a predetermined format on a standard image display apparatus such as a television set, the pixels of the frame being reproduced not simultaneously but sequentially. More particularly, adjacent pixels are written consecutively so as to write a horizontal line and the horizontal lines of the frame are written consecutively (interlaced). The time thus required for reproducing one frame, i.e. the time required to write all the image lines making up the frame, is {fraction (1/25)} s in the PAL format. Consequently, a scene whose actual playing time is 100 s corresponds to a sequence of 2500 consecutive frames.
For recording video images on a carrier, such as for example a magnetic tape, an analog method is known in which the consecutive pixels are recorded adjacent one another on recording tracks which are inclined with respect to the playing direction of the carrier. Each recording track then corresponds to one image line. With recordings of this type the possibilities for slow-motion or fast-motion reproduction are limited. For example, when it is desired to reproduce a scene at five times the normal speed, the carrier is moved past a read head at five times the normal speed. This means that five consecutive images move past the read head in the time required for the reproduction of a single image by the image display apparatus. An image reproduced on the display screen then takes the form of five fragments of these five consecutive images, which fragments are displayed one above the other and are separated from one another by distorted image portions.
More recently, a digital recording method termed MPEG has been developed. In this method the information relating to an image is digitally coded and compressed and is linearly stored on a carrier, which is to be understood to mean that the consecutive bits are arranged in line with one another in the write and read direction of the carrier.
When such a recording is played back the bits being read do not correspond to the pixels of a frame to be reproduced consecutively. A multiplicity of bits must be collected in order to be decoded and in order to reconstruct the image content of one or more consecutive frames. The buffer memories and computing devices required for this may be provided in the playback apparatus or in the display apparatus. It is to be noted, though, that on an average the number of bits read corresponds to 25 frames per second at a normal playback speed of the carrier. In principle, it is possible to move the carrier more rapidly or slowly past the read head. However, the problem is that a standard display apparatus such as a television set is not capable of converting the signals then received to normal frames.
It is an object of the present invention to provide a method and an arrangement which enable a video recording made in accordance with an MPEG method to be reproduced with a playback speed which is adjustable within ample margins on a standard display apparatus such as a television set.
More particularly, it is an object of the present invention to allow the user of such a playback arrangement to vary the playback speed almost continuously between slow-motion and fast-motion reproduction.